1. Field of the Invention
This invention relates in general to film resistors and more particularly to a method of forming a universal film resistor for hybrid circuits.
2. Description of the Prior Art
Film resistors are commonly used in hybrid circuits and include thick film resistors which are conventionally formed by screen-printing a resistive material on an insulating substrate and then firing the material, and thin film resistors which are conventionally formed by sputtering or vacuum-depositing a resistive material on an insulating substrate.
In hybrid circuits it is often necessary to adjust the resistance of the film resistors in the circuit. To increase the resistance of a film resistor, the resistor is "trimmed" by forming a slot across the electrical current path in the resistor to make the effective width of the resistor smaller and thereby increased resistance. The channel may be formed by mechanical abrasion, chemical etching, or laser vaporization of the resistor material.
At present, film resistors for hybrid circuits require resistive material of different ranges and values. The final resistance value depends on the aspect ratio of the resistor and the sheet resistivity of the resistive material. When a wide range of values is required in the manufacture of a hybrid circuit the deposition of resistor material must be repeated for each different range of value of resistance. Such resistors are processed to lower values than the circuit calls for and after completion of the manufacturing process are trimmed up in value to the resistance required in the circuit.
This method has been found to be costly and time consuming in manufacturing hybrid film circuits because of the two or more different resistor compositions required.
Accordingly, it is the object of the present invention to provide a method of manufacturing a film resistor, employing one resistor composition that can be trimmed to any value from 0 ohms to an infinite resistance for a film hybrid circuit.